This invention relates to an improved positive displacement gas meter including a simplified composite center casting including center chamber casting and a valve chamber manifold casting providing mounting support for the diaphragm linkage and crank assembly.
Positive displacement gas meters are well-known in the art and are manufactured by, among others, Sprague Meter Division of Textron, Inc., assignee of this application. FIGS. 7 and 8 of the drawings herein illustrate a prior art positive displacement gas meter 100. The gas meter 100 generally comprises a center casting 110 which is generally cylindrical and defines a center chamber 111. A front cover 130 is mounted to the front side of the center casting 110, and the peripheral edge 133 of a front diaphragm 135 is clamped between the front cover and the center casting. Thus, a front chamber 136 is defined between the front cover and the front diaphragm. Similarly, a rear cover 140 is mounted to the opposite rear side of the center casting 110, clamping the peripheral edge 143 of a rear diaphragm 145 therebetween and defining a rear chamber 146.
The upper portion of the center casting 110, generally designated at 112 and also seen in top plan view in FIG. 8, is a relatively complex configuration defining passages, etc. More particularly, the upper portion 112 of the center casting 110 defines an L-shaped passage 113 which is aligned with a passage 131 formed in the front cover 130 to provide gas communication with the front chamber 136. A similar L-shaped passage 114 defined by the upper portion of the center casting is aligned with passage 141 in the rear cover 140 to provide gas communication with the rear chamber 146. A passage 115 (see FIG. 8) is provided to the center chamber 111, and a manifold passage 116 leads to an outlet 117. The bottom wall 118 of the manifold passage 116 is provided with a threaded sleeve 119. A support bracket 120 is threadably received in the sleeve 119, and the bracket 120 carries a main shaft 121 having a diaphragm linkage assembly 122 mounted to the lower end thereof. The diaphragm linkage assembly 122 includes levers, wire brackets pivotally mounted to the levers and to the diaphragms, all connecting the front and rear diaphragms such that the center shaft 121 is rotated as the gas meter operates.
The top surface of the center casting 110, designated by the number 123 in FIG. 8, is planar and mounts a valve seat 125. The valve seat 125 has openings which connect with the passages 113-116 of the center casting 110. The valve seat 125 also mounts a bearing passing the main shaft 121. A valve cover 127, having a recessed annular cavity 128, is slidably mounted on the valve seat 125 and is driven in a circular motion thereon by a crank and offset crank pin 129 connected to the main shaft 121.
A top casting 150 is also mounted to the center casting 110, and the top casting 150 mounts a meter readout assembly very generally indicated at 151, the meter drive being taken from the circular motion of the valve cover 127. The top casting 150 also mounts an inlet 152 wherein gas is input to the meter, and defines an outlet passage (not shown) which connects with outlet 117 of the manifold passage 116 of the center casting 110.
In operation, the incoming gas is sequentially directed to one of the front, center and rear chambers as the valve cover moves in its circular path opening the various passages to the chambers, and gas is also expelled from the meter as the annular cavity of the valve cover connects the passages to the chambers with the manifold passage 116 leading to outlet 117. In particular, as a chamber fills with gas, it expands its diaphragm, thereby emptying an adjacent chamber, and the movement of the diaphragm rotates the shaft 121 to revolve the valve seat and maintain continual operation. The meter readout 151 is driven by the rotating valve cover.
The center casting in the above described gas meter is generally cast from iron or aluminum. An iron casting is more rugged, however, the intricacies of the casting make it both difficult and expensive to manufacture. Additionally, accuracy of the center casting is also difficult to achieve because of its complexity, and in particular, it is somewhat difficult to achieve precise alignment of the various passages to achieve good alignment of the operating mechanism (the main shaft and diaphragm linkage and crank assemblies) and to achieve dependable sealing.